Fixes <http://webkit.org/b/43197> WebKit2 often says "plugin
directory" when it means "plugins directory"

Reviewed by John Sullivan.

WebKit2:

* UIProcess/API/C/WKContext.cpp:
(_WKContextSetAdditionalPluginsDirectory):
* UIProcess/API/C/WKContextPrivate.h:
Renamed from _WKContextSetAdditionalPluginDirectory.

* UIProcess/Plugins/PluginInfoStore.cpp:
(WebKit::PluginInfoStore::setAdditionalPluginsDirectories): Renamed
from setAdditionalPluginDirectories.
(WebKit::PluginInfoStore::loadPluginsIfNecessary): Updated for rename.

* UIProcess/Plugins/PluginInfoStore.h: Renamed
m_additionalPluginDirectories to m_additionalPluginsDirectories.

* UIProcess/Plugins/mac/PluginInfoStoreMac.mm:
(WebKit::PluginInfoStore::pluginsDirectories):
* UIProcess/Plugins/qt/PluginInfoStoreQt.cpp:
(WebKit::PluginInfoStore::pluginsDirectories):
* UIProcess/Plugins/win/PluginInfoStoreWin.cpp:
(WebKit::PluginInfoStore::pluginsDirectories):
Renamed from pluginDirectories.

* UIProcess/WebContext.cpp:
(WebKit::WebContext::setAdditionalPluginsDirectory):
* UIProcess/WebContext.h:
Renamed from setAdditionalPluginDirectory.

WebKitTools:

* WebKitTestRunner/TestController.cpp:
(WTR::TestController::initialize): Updated for rename.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@64287 268f45cc-cd09-0410-ab3c-d52691b4dbfc